This is an inevitable question for engineers working on building automation and HVAC system integration. Domestic PLCs are budget-friendly, but how reliable are they? Imported PLCs come with a higher price tag — so what makes them worth the extra cost? We ran a comprehensive system comparison on real projects, and will share our practical test results today.

The test was conducted on the central air conditioning control system of a large commercial complex. The controlled devices include chiller unit start/stop, variable frequency control for chilled water pumps, interlock control of air handling units, and indoor temperature & humidity regulation.

The system integrates 68 analog points and 42 digital points in total.

We selected two mainstream small-to-medium PLCs with similar product positioning for the comparison:

• Siemens S7-1200 (representative imported PLC)
• Inovance H5U (representative domestic PLC)

The price of the imported model is approximately three times that of the domestic one.

Both models achieve similar performance in temperature PID control, with the steady-state error kept within ±0.3°C for both.

The Siemens PLC responds slightly faster under high-frequency operating conditions. Nevertheless, this tiny gap is hardly perceptible in regular HVAC systems and has no impact on overall control performance.

Siemens TIA Portal boasts a mature ecosystem and abundant function block libraries, delivering a seamless online debugging experience.

Inovance AutoShop has been updated rapidly in recent years and now covers nearly all mainstream functions with no obvious deficiencies. However, its third-party resource library is still less extensive than Siemens’.

Engineers with prior experience using Siemens products usually need 1 to 2 weeks to get familiar with domestic PLCs. Overall, the learning cost is acceptable.

Both units support mainstream protocols including BACnet, Modbus RTU/TCP and MQTT, which meet the requirements of most common application scenarios.

Difficulties mainly occur when connecting to sensors of legacy brands. Siemens is equipped with a more complete driver library, while domestic PLCs sometimes require manual compilation of communication messages, which will prolong the commissioning period. This is a common problem encountered on construction sites. Being aware of it in advance can help you avoid many pitfalls.

After six months of continuous operation, neither PLC experienced unexpected restarts or disconnection failures, showing equally reliable performance.

The stability of domestic PLCs in high-temperature equipment rooms (above 40°C) has improved significantly in recent years. The once-concerning heat dissipation issues have been largely resolved, and are no longer a major consideration for product selection.

1. For new projects with tight budgets and a team open to learning new tools: Choose domestic PLCs. They offer remarkable overall cost advantages and work perfectly for HVAC control scenarios.
2. For renovation projects with existing Siemens systems or brands designated by clients: Stick to imported PLCs. This avoids extra schedule losses caused by system incompatibility and prioritizes operational stability.
3. For export projects or applications requiring CE certification: Prioritize imported PLCs. Domestic products still face long lead times for international certification, and it is not advisable to take risks in this regard.

Domestic PLCs have achieved tangible progress over the years and are fully competent for HVAC control applications. The core competitive edge of imported brands has shifted from basic functionality to accumulated ecosystem resources and brand credibility.

Your final choice should depend on the actual conditions of your project, rather than price alone.

Feel free to leave a message if you have any questions about engineering product selection.